I'd like to use GPU OpenCL acceleration (afaik OpenCL on NPU isn't supported at all for now?) on headless armbian and I'm getting "No devices found in platform" in clinfo.

Could you clarify whether armbian has support for this and I'm missing something (kernel flags? userspace driver? some kinda nonfree blob?), or there's no support and I should move onto another distro? Thanks

To my knowledge Armbian has no support for the NPU side of things. Only (some) vendor Khadas images have this with example code. It all doesn't work as I'd like to see it, no compatibility with known standards. 
In my opinion the NPU is kind of useless. And Khadas isn't a big help here. Maybe LibreComputers has better implementation for it...

I understand that, my original question was about using the GPU for OpenCL applications